Hyaluronate production by the inner ear during otic capsule and perilymphatic space formation

Otosclerosis has been hypothesized to result from a disorder of the extracellular matrix of the cartilaginous rests present in the adult temporal bone. Matrix relationship to bone formation and remodeling, as well as the fact that the pathogenesis of otosclerosis is expressed by the action of both of these processes, strongly suggests that more knowledge is needed about the process of otic capsule development. In pursuit of this goal, otic complexes were explanted from mouse embryos that ranged in age from 10.5 to 16 days old and were then exposed to ³H-glucosamine (50 μCi/ml) for 6 hours in vitro. Total labeled glycosaminoglycans (GAGs) and labeled hyaluronate content of each age group of otic explants were measured, and the results were compared to a developmental series of the otic regions of whole embryos stained with either toluidine blue or alcian blue. Increases in the synthesis of the total GAGs were observed on embryonic day 11 and for a prolonged period extending from gestation day 13.5 through day 16. The first increase of GAGs occurred at the initiation of metachromasia and positive staining by toluidine blue of the region of aggregated periotic mesenchyme cells that form the otic capsule. The second increase in GAGs was correlated with chondrification of the capsule. Hyaluronate production revealed a different pattern. Synthesis of hyaluronate exhibits peaks at 10.5, 12.5, and for an extended period of from 13.5 to 14.5 days of gestation. Histologic evidence suggested that the 10.5-day peak is probably associated with migration of mesenchyme cells into the periotic region, the 12.5-day peak with inhibition of further cellular aggregation, and the 13.5- to 14.5-day peak with the onset of otic capsule chondrification and perilymphatic space formation. Alcian blue histochemistry confirmed the presence of hyaluronate in both the extracellular matrix of the cartilaginous otic capsule and the presumptive perilymphatic spaces during their formation. The results suggest that hyaluronate is involved in control of both otic capsule and perilymphatic space formation.